When an ink pen of a thermal inkjet printer containing relatively heavy pigmented particles disbursed in a relatively light unpigmented fluid vehicle has been stored for a long period of time in other than its normal upright position, there will be a tendency for some of the pigmented particles to migrate out of the nozzle chamber. When such a pen is first placed into service, the initial print drops will thus be slightly smaller and lighter than normal. After the individual nozzles have been fired a certain number of times, any relatively unpigmented liquid in the vicinity of the nozzles will have been discharged and/or the pigments will have been more uniformly distributed and the pen will begin to print in the normal optical density. As a result, the print quality achievable with a newly installed pen may be uneven and unpredictable. Particularly if the pen and/or the printer is new and the user in not familiar with such a possible unevenness in print quality, the user may think that the pen and/or the printer is defective, thereby causing consumer dissatisfaction and unnecessary warranty claims and service calls.
Some prior art printers perform, each time they are turned on and/or prior to printing each page, one or more ink ejection ("spitting") and/or other servicing operations ("priming" and/or "wiping") to preheat and clean the individual nozzles and to clear viscous plugs therefrom; however, such routine servicing may not be sufficient to ensure that the ink in the vicinity of the nozzles of a new or newly-installed pen is properly mixed. In some prior art printers, certain nozzle clearing operations are performed whenever an inspection door has been manually opened and closed. In any event, if sufficient ink ejections to completely eliminate any poorly pigmented liquid in the vicinity of the nozzle chamber are made each time the printer is turned on and/or each time the inspection door is opened, a large quantity of ink will be unnecessarily wasted.